In future, some other cryptocurrencies may come close to bitcoin in terms of market size. What I am not sure of is whether this generation will witness such a development where another cryptocurrency will topple bitcoin. Bitcoin will reign for a very long time or maybe forever.
The future is hidden and only God knows what will happen in the future. We can just predict the future price and mostly our predictions become wrong because we dont know how many people will enter and how many will quit, and the price depends upon the investment cap. The more the investment the high will be the price. It is simple and nothing complicated in it.